Even before the release of the iPhone X, Face ID - a facial recognition feature which replaced Touch ID - was under criticism for a number of reasons. Its inability to differentiate between twins, and that facial recognition technology with reduced accuracy apparently might have been pushed out to decrease manufacturing costs are just a couple of reasons some iPhone users might still prefer Touch ID.
Recently, users on Apple's support forums reported that they find themselves unable to approve family purchase requests on their iPhone X using Face ID, even though they were previously able to do so. Instead, the person who is supposed to authorize family purchases on Ask to Buy must enter his or her Apple account password. Incidentally, Ask to Buy is an iOS feature which enables parents to keep a check on their children's purchases.
Entering a password can be understandably cumbersome for many consumers, as people tend to use complicated passwords to improve security. Typing out a complex password each time one receives a purchase request from a family member isn't efficient, which especially pertains to people with large families. Furthermore, it appears that former Apple devices still allow users to approve these purchases through the use of Touch ID, so it seems that this is a specific problem with regards to the iPhone X and Face ID combination.
Importantly, the official documentation for Ask to Buy does not mention any use of Face ID or Touch ID. It might be surprising for many iPhone users that Apple did not implement facial authentication for one of its own iOS features, especially since third-party applications using Touch ID smoothly transitioned to Face ID on the iPhone X. However, considering a 10-year-old was apparently able to unlock his mother's phone using Face ID recently, even though the facial recognition system was set up for the mother, one can only wonder how secure that would have been.
Apple has yet to clarify why this limitation is present when approving purchases on the iPhone X using the Ask to Buy feature.
Via Ars Technica